package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.util.ToStringUtils;

import java.io.IOException;
import java.util.Set;

/**
 * A query that applies a filter to the results of another query.
 *
 * <p>Note: the bits are retrieved from the filter each time this
 * query is used in a search - use a CachingWrapperFilter to avoid
 * regenerating the bits every time.
 *
 * <p>Created: Apr 20, 2004 8:58:29 AM
 *
 * @since   1.4
 * @see     CachingWrapperFilter
 */
public class FilteredQuery extends Query {

    Query query;
    Filter filter;

    /**
     * Constructs a new query which applies a filter to the results of the original query.
     * Filter.getDocIdSet() will be called every time this query is used in a search.
     * @param query  Query to be filtered, cannot be <code>null</code>.
     * @param filter Filter to apply to query results, cannot be <code>null</code>.
     */
    public FilteredQuery(Query query, Filter filter) {
        this.query = query;
        this.filter = filter;
    }

    /**
     * Returns a Weight that applies the filter to the enclosed query's Weight.
     * This is accomplished by overriding the Scorer returned by the Weight.
     */
    @Override
    public Weight createWeight(final Searcher searcher) throws IOException {
        final Weight weight = query.createWeight(searcher);
        final Similarity similarity = query.getSimilarity(searcher);
        return new Weight() {
            private float value;

            // pass these methods through to enclosed query's weight
            @Override
            public float getValue() {
                return value;
            }

            @Override
            public boolean scoresDocsOutOfOrder() {
                return false;
            }

            public float sumOfSquaredWeights() throws IOException {
                return weight.sumOfSquaredWeights() * getBoost() * getBoost(); // boost sub-weight
            }

            @Override
            public void normalize(float v) {
                weight.normalize(v * getBoost()); // incorporate boost
                value = weight.getValue();
            }

            @Override
            public Explanation explain(IndexReader ir, int i) throws IOException {
                Explanation inner = weight.explain(ir, i);
                Filter f = FilteredQuery.this.filter;
                DocIdSet docIdSet = f.getDocIdSet(ir);
                DocIdSetIterator docIdSetIterator = docIdSet == null ? DocIdSet.EMPTY_DOCIDSET.iterator() : docIdSet.iterator();
                if (docIdSetIterator == null) {
                    docIdSetIterator = DocIdSet.EMPTY_DOCIDSET.iterator();
                }
                if (docIdSetIterator.advance(i) == i) {
                    return inner;
                } else {
                    Explanation result = new Explanation(0.0f, "failure to match filter: " + f.toString());
                    result.addDetail(inner);
                    return result;
                }
            }

            // return this query
            @Override
            public Query getQuery() {
                return FilteredQuery.this;
            }

            // return a filtering scorer
            @Override
            public Scorer scorer(IndexReader indexReader, boolean scoreDocsInOrder, boolean topScorer) throws IOException {
                // Hackidy-Häck-Hack for backwards compatibility, as we cannot change IndexSearcher API in 3.x, but still want
                // to move the searchWithFilter implementation to this class: to enable access to our scorer() implementation
                // from IndexSearcher, we moved this method up to the main class. In Lucene trunk,
                // FilteredQuery#getFilteredScorer is inlined here - in 3.x we delegate:
                return FilteredQuery.getFilteredScorer(indexReader, similarity, weight, this, filter);
            }
        };
    }

    /** Hackidy-Häck-Hack for backwards compatibility, as we cannot change IndexSearcher API in 3.x, but still want
     * to move the searchWithFilter implementation to this class: to enable access to our scorer() implementation
     * from IndexSearcher without instantiating a separate {@link Weight}, we make the inner implementation accessible.
     * @param indexReader the atomic reader
     * @param similarity the Similarity to use (deprecated)
     * @param weight the weight to wrap
     * @param wrapperWeight must be identical to {@code weight} for usage in {@link IndexSearcher}, but it is different inside this query
     * @param filter the Filter to wrap
     * @lucene.internal
     */
    static Scorer getFilteredScorer(final IndexReader indexReader, final Similarity similarity, final Weight weight, final Weight wrapperWeight, final Filter filter) throws IOException {
        assert filter != null;

        final DocIdSet filterDocIdSet = filter.getDocIdSet(indexReader);
        if (filterDocIdSet == null) {
            // this means the filter does not accept any documents.
            return null;
        }

        final DocIdSetIterator filterIter = filterDocIdSet.iterator();
        if (filterIter == null) {
            // this means the filter does not accept any documents.
            return null;
        }

        // we are gonna advance() this scorer, so we set inorder=true/toplevel=false
        final Scorer scorer = weight.scorer(indexReader, true, false);
        return (scorer == null) ? null : new Scorer(similarity, wrapperWeight) {
            private int scorerDoc = -1, filterDoc = -1;

            // optimization: we are topScorer and collect directly using short-circuited algo
            @Override
            public void score(Collector collector) throws IOException {
                int filterDoc = filterIter.nextDoc();
                int scorerDoc = scorer.advance(filterDoc);
                // the normalization trick already applies the boost of this query,
                // so we can use the wrapped scorer directly:
                collector.setScorer(scorer);
                for (;;) {
                    if (scorerDoc == filterDoc) {
                        // Check if scorer has exhausted, only before collecting.
                        if (scorerDoc == DocIdSetIterator.NO_MORE_DOCS) {
                            break;
                        }
                        collector.collect(scorerDoc);
                        filterDoc = filterIter.nextDoc();
                        scorerDoc = scorer.advance(filterDoc);
                    } else if (scorerDoc > filterDoc) {
                        filterDoc = filterIter.advance(scorerDoc);
                    } else {
                        scorerDoc = scorer.advance(filterDoc);
                    }
                }
            }

            private int advanceToNextCommonDoc() throws IOException {
                for (;;) {
                    if (scorerDoc < filterDoc) {
                        scorerDoc = scorer.advance(filterDoc);
                    } else if (scorerDoc == filterDoc) {
                        return scorerDoc;
                    } else {
                        filterDoc = filterIter.advance(scorerDoc);
                    }
                }
            }

            @Override
            public int nextDoc() throws IOException {
                filterDoc = filterIter.nextDoc();
                return advanceToNextCommonDoc();
            }

            @Override
            public int advance(int target) throws IOException {
                if (target > filterDoc) {
                    filterDoc = filterIter.advance(target);
                }
                return advanceToNextCommonDoc();
            }

            @Override
            public int docID() {
                return scorerDoc;
            }

            @Override
            public float score() throws IOException {
                return scorer.score();
            }
        };
    }

    /** Rewrites the wrapped query. */
    @Override
    public Query rewrite(IndexReader reader) throws IOException {
        Query rewritten = query.rewrite(reader);
        if (rewritten != query) {
            FilteredQuery clone = (FilteredQuery) this.clone();
            clone.query = rewritten;
            return clone;
        } else {
            return this;
        }
    }

    public Query getQuery() {
        return query;
    }

    public Filter getFilter() {
        return filter;
    }

    // inherit javadoc
    @Override
    public void extractTerms(Set<Term> terms) {
        getQuery().extractTerms(terms);
    }

    /** Prints a user-readable version of this query. */
    @Override
    public String toString(String s) {
        StringBuilder buffer = new StringBuilder();
        buffer.append("filtered(");
        buffer.append(query.toString(s));
        buffer.append(")->");
        buffer.append(filter);
        buffer.append(ToStringUtils.boost(getBoost()));
        return buffer.toString();
    }

    /** Returns true iff <code>o</code> is equal to this. */
    @Override
    public boolean equals(Object o) {
        if (o instanceof FilteredQuery) {
            FilteredQuery fq = (FilteredQuery) o;
            return (query.equals(fq.query) && filter.equals(fq.filter) && getBoost() == fq.getBoost());
        }
        return false;
    }

    /** Returns a hash code value for this object. */
    @Override
    public int hashCode() {
        return query.hashCode() ^ filter.hashCode() + Float.floatToRawIntBits(getBoost());
    }
}
